Relationship between antioxidant activity and ESIPT process based on flavonoid derivatives: A comprehensive analysis

Antioxidant activity, as a topic of current interest, is discussed together with the excited state intramolecular proton transfer (ESIPT) process for three flavonoid derivatives, based on density functional theory (DFT)and time-dependent DFT (TD-DFT) methods, as well as DPPH free radical scavenging assay. The potential energy curves and transition states demonstrate that the three molecules can undergo only single proton transfer in the excited state, and all of them are ultrafast ESIPT processes. The absorption spectra of all the molecules show effective protection against UV radiation with low fluorescence intensity, especially Baicalein (Bai), which demonstrates their great potential for sunscreen applications. The density of states, HOMO energy values, global and local indices reveal that the antioxidant activity of the molecules after ESIPT process is enhanced, with Bai having the highest antioxidant activity, which is significantly attributed to the number and position of phenolic hydroxyl groups. Moreover, by comparing the DPPH free radical scavenging activity under the dark and UV radiation conditions, the radical scavenging activity (RSA) value in the UV radiation is remarkably higher than that in the dark condition, in which Bai achieves RSA value of 93.4%. Overall, the antioxidant activity of all three ESIPT-based flavonoid derivatives, especially Bai, is significantly elevated in the keto* form, which reinforces the significant relationship between antioxidant activity and ESIPT process, and provides new application prospects for molecules with ESIPT properties.

Trimetallic MOF-derived Fe-Mn-Sn oxide heterostructure enabling exceptional catalytic degradation of organic pollutants

Developing efficient and environmentally benign heterogeneous catalysts that activate peroxymonosulfate (PMS) for the degradation of persistent organic contaminants remains a challenge. Metal-organic frameworks (MOFs)-derived metal oxide catalysts in advanced oxidation processes (AOPs) have received considerable attention research fraternity. Herein, we report an innovative magnetic trimetallic MOF-derived Fe-Mn-Sn oxide heterostructure (FeMnO@Sn) with adjustable morphology, size and Sn content, prepared through an impregnation-calcination strategy. The formation of a novel magnetic Fe2O3/Fe3O4/Mn3O4 heterostructure induces the generation of abundant Fe2+ and Mn2+ sites on the FeMnO@Sn surface. Meanwhile, the introduction of SnO2 into the Fe2O3/Fe3O4/Mn3O4 heterostructure facilitates the cleavage of the OO bond in adsorbed PMS. The synergy among the different functionalities of each metal oxide plays a vital role in the swift and effective degradation of pollutants. In addition, the uniquely designed catalyst exhibits magnetic properties that facilitate easy recycling and repeated use, thereby meeting environmental protection requirements. Overall, this research highlights the design of heterogeneous catalysts for the effective activation of PMS and provides valuable insights for the advancement of future environmental catalysts.

Advances in Organic Fluorescent and Colorimetric Probes for The Detection of Cu2+ and Their Applications in Cancer Cell Imaging (2020-2024)

Organic fluorescence and colorimetric probes have emerged as vital tools for detecting metal ions, due to their high sensitivity, selectivity, and rapid response times. Copper, an essential trace element, plays a critical role in biological systems, yet its imbalance can lead to severe disorders such as neurodegenerative diseases, cancer, and Wilson's disease. Over the past few years, advancements in probe design have unlocked innovative avenues for not only detecting Cu2+ in environmental and biological samples but also for visualizing its distribution through fluorescence imaging. These probes offering robust performance under diverse conditions. Fluorescence imaging using these probes plays a pivotal role in cancer diagnosis, prognosis, and treatment monitoring by offering real-time visualization of tumor morphology and biomolecular interactions at cellular and tissue levels. This review aims to explore the diversity of organic fluorescence and colorimetric probes developed for the detection of Cu2+, with a particular focus on their applications in fluorescence imaging from 2020 to 2024. The discussion highlights the use of these probes in visualizing Cu2+ in various cancer cells such as SiHa, HCT 116, GES-1, RAW 264.7, HepG2, HeLa, MCF-7 and DrG cell lines, tissues, and small living organisms. By targeting cancer-specific pathways and monitoring copper-related physiological changes, these probes have significantly advanced the fields of cancer diagnostics and therapeutics. This comprehensive analysis emphasizes the potential of fluorescence imaging as a powerful tool for elucidating the roles of Cu2+ in health and disease, paving the way for future advances in biomedical research.

Elaborating H-bonding effect and excited state intramolecular proton transfer of 2-(2-hydroxyphenyl)benzothiazole based D-π-A fluorescent dye

2-(2-Hydroxyphenyl)benzothiazole (HBT) derivatives with donor-π-acceptor (D-π-A) structure have received extensive attention as a class of excited state intramolecular proton transfer (ESIPT) compounds in the fields of biochemistry and photochemistry. The effects of electron-donors (triphenylamine and anthracenyl), the position of substituents and solvent polarity on the fluorescence properties and ESIPT mechanisms of HBT derivatives were investigated through time-dependent density functional theory (TDDFT) calculations. Potential energy curves (PECs) and frontier molecular orbitals (FMOs) reveal that the introduction of the triphenylamine group on the benzene ring enhances intramolecular HB, thereby benefiting the ESIPT process. Analysis of their spectra reveals that P-TPA (para position for TPA) and M-TPA (meta position for TPA) are both excellent candidates for fluorescent dyes because of their large Stokes shifts. The PECs of four derivatives indicate that the ESIPT process of P-TPA in dimethyl sulfoxide (DMSO) solvent is the most likely to occur. The research revealed that both P-TPA and P-En (para positions for both TPA and En) can undergo a spontaneous transformation from the enol to the keto form in the S1 state. Furthermore, the ESIPT process was found to be enhanced with an increase in polarity. The energy barrier of P-TPA(N*) → P-TPA(K*) is 3.06 kcal mol-1 in the S1 state and its reversed energy barrier is 4.47 kcal mol-1. The para triphenylamine group could accelerate the ESIPT reactions, as it has a greater impact on the excited state intramolecular hydrogen bond (ESIHB) compared to meta-substitution of the triphenylamine group.

External electric field induced emission behavior for ESIPT-based 2-(benzo[d]thiazol-2-yl)-4-(pyren-1-yl)phenol towards near-infrared region

Organic light-emitting diodes (OLEDs) for low energy transfer and double emission, but the current methods for regulating ESIPT processes are mostly solvent and substituent effects. Here, utilizing the density theory functional (DFT) and time-dependent density functional theory (TD-DFT) methods, the ESIPT process controlled by an external electric field (EEF) is proposed, and the changes in photophysical properties of 2-(benzo[d]thiazol-2-yl)-4-(pyren-1-yl)phenol (PyHBT) are investigated. Structural parameter variations and IR vibrational spectra measure the prerequisite for the ESIPT process, namely, intramolecular hydrogen bond (IHB) strength, and the scanned potential energy curves (PECs) demonstrate that the ESIPT process of PyHBT is harder to execute as the positive EEF increases, and the opposite is true for the negative EEF. The absorption and fluorescence spectra show shifts under the distinct EEFs, and even the emission wavelength reaches the short-wave near-infrared (SW-NIR) region (780-1100 nm), such as 815.2 nm for a positive EEF of + 30 × 10-4 a.u. in the keto form. Additionally, the fluorescence intensity of PyHBT is strongly influenced by the positive EEF, especially in the enol form, and the investigation of the mechanism by hole-electron analysis demonstrates that under the positive EEF, the twisted intramolecular charge transfer (TICT) process is induced, which triggers the weakening of the fluorescence intensity. In summary, our work not only complements the theoretical approach to modulate the ESIPT process, but also reveals that the photophysical properties of materials affected by the external electric field are even expected to reach the NIR region.

Construction of a sequence activated fluorescence probe for simultaneous detection of γ-glutamyl transpeptidase and peroxynitrite in acute kidney injury

Acute kidney injury (AKI) can result in a sudden decline in kidney function and, if not promptly diagnosed and treated, can lead to a high mortality rate. Therefore, there is a critical need for the development of a non-invasive and dependable early diagnostic method for AKI to prevent its progression and deterioration. To address the risk of misdiagnosis or overlooked diagnosis due to reliance on a single biomarker, we developed a novel molecular fluorescent probe (HX-GP) to simultaneously detect and image two biomarkers, γ-Glutamyl transpeptidase (γ-GGT) and Peroxynitrite (ONOO-), in the AKI process. HX-GP can specifically detect γ-GGT in the red fluorescence channel (λem = 613 nm) and ONOO- in the green fluorescence channel (λem = 518 nm). HX-GP demonstrated high sensitivity, selectivity, and rapid response, showing excellent biocompatibility and detection performance. In addition, HX-GP was successful in imaging experiments in a cell model of cisplatin-induced AKI, a result that highlights its potential application value in early diagnosis of AKI.

Electronic Substitution Effect on ESIPT-Driven pH and Amine Sensing: Exploring Mechanism

It is required to have a more straightforward and easier way to check the quality of food to ensure the safety of the public health. The decomposition of meat protein results in ammonia and biogenic amines (BAs). Consequently, to evaluate the safety and quality of meat products throughout the storage, transit, and consumption depends on the sensitive detection of the released BAs. Here, we have designed and synthesized three luminescent-based probe molecules, which originated from 2-(2-hydroxyphenyl) benzothiazole (HBT) derivatives and showed the excited state-induced proton transfer (ESIPT) phenomenon. The two substituents (OMe and NO2) were used rationally at the para position of HBT, and the electronic properties were evaluated using Hammett substituent constants. The proton donating ability of the O-H to the acceptor is largely facilitated by the presence of a strong electron-withdrawing group, which in this case is NO2. The proton transfer rate can be controlled, and in this case, to a slower rate with the influence of the electron donating group OMe. The controllability of proton transfer led us to use it in pH sensing. A prominent and multi-color change with pH variation was observed in the case of the OMe substituted compound. These probes were further employed for amine sensing, and the limit of detection (LOD) was determined to be 28.6 μM and 61.34 nM for ammonia and hydrazine, respectively. In addition, strip-based detection of spoilage of chicken meat was studied for real-world applications via both contact and non-contact modes.

Recent Advances in Fluorescent Based Chemical Probes for the Detection of Perchlorate Ions

This review highlights recent advancements and challenges in fluorescence-based chemical sensors for selective and sensitive detection of perchlorate, a persistent environmental pollutant and global concern due to its health and safety implications. Perchlorate is a highly persistent inorganic pollutant found in drinking water, soil, and air, with known endocrine-disruptive properties due to its interference with iodide uptake by the thyroid gland. Human exposure mainly occurs through contaminated water and food. Additionally, perchlorates are prevalent in improvised explosives, causing numerous civilian casualties, making their detection important in a worldwide aspect. Fluorescence-based chemical sensors provide a valuable tool for the selective detection of perchlorate ions due to their simplicity and applicability across various fields, including biology, pharmacology, military, and environmental science. This review article overviews perchlorate chemistry, occurrence, and remediation strategies, compares regulatory limits, and examines fluorescence-based detection mechanisms. It systematically summarizes recent advancements in designing at least a dozen fluorescence-based chemical materials for detecting perchlorate in the environment over the past decade. Key focus areas include the design and molecular architecture of synthetic chemical chromophores for perchlorate sensing and the photochemistry mechanisms driving their effectiveness. The main findings indicate that there has been significant progress in the development of reliable and robust fluorescence-based sensors with higher selectivity and sensitivity for perchlorate detection. However, several challenges remain, such as improving detection limits and sensor stability. The review outlines potential future research directions, emphasizing the need for further innovation in sensor design and development. It aims to enhance understanding and spur advances that could create more efficient and robust chemical scaffolds for perchlorate sensing. By addressing current limitations and identifying opportunities for improvement, the review provides a comprehensive resource for researchers working to develop better detection methods for this significant environmental pollutant.

Dual-mode luminescence and colorimetric sensing for Al3+ and Fe2+/Fe3+ ions in water using a zinc coordination polymer

A zinc(II) coordination polymer, [Zn(H2dhtp)(2,2'-bpy)(H2O)]n (1), has been utilized as a dual-mode luminescence-colorimetric sensor (H2dhtp2- = 2,5-dihydroxy terephthalate and 2,2'-bpy = 2,2'-bipyridine). The presence of hydroxyl groups in H2dhtp2- can promote excited-state intra- and intermolecular proton transfer (ESIPT) phenomena. Therefore, compound 1, which displays high stability in aqueous environments, exhibits a strong green-yellow photoluminescence. This luminescence signal can be considerably enhanced and blue-shifted upon the addition of Al3+ ions with a limit of detection (LOD) of 0.15 μM, and it demonstrates significant resistance to interference from several competing metal ions. To demonstrate a practical application, 1@paper strips were fabricated that can visually detect the Al3+ ion under a UV lamp. Moreover, 1 can detect either Fe2+ or Fe3+ ions in aqueous solutions by a visible color shift. Upon the incremental addition of Fe2+ or Fe3+ ions, the solution color changed from colorless to pink, exhibiting a pronounced absorption band at around 521 nm. The LODs were determined to be 1.55 and 0.34 μM for Fe2+ and Fe3+, respectively. Furthermore, compound 1 was used for the determination of Fe3+ ions in the real water samples, which can be evaluated on-site in real-time via a smartphone color-scanning application. The detection efficacy of 1 toward Al3+ and Fe2+/Fe3+ maintains significant luminescence stability and reusability.

Fast tracking of Hg2+ ions in living cells, food, and environmental samples using a new mitochondria-targeted red emitting probe and its portable applications

Mercury is one of the most hazardous heavy metals and is capable of biomagnification, thereby posing severe risks to ecosystems and human health. Therefore, selective, sensitive, and rapid detection of Hg2+ in a wide range of samples is essential. Herein, we report the synthesis of a new 2-(benzo[d]thiazol-2-yl) phenol-based fluorescent probe (PyS) and its potential as a fluorescent probe for detecting Hg2+ ions in various real samples such as rice, garlic, shrimp, and root samples. When interacting with Hg2⁺, the non-fluorescent probe solution emitted strong red fluorescence at 638 nm in a solution of DMSO/H2O (1/9, v/v). The other ions showed no significant interference during Hg2+ detection. In addition, PyS displayed a rapid response time among the reaction-based systems (3-4 min), low detection limit (72.5 nM), linear response trend in the range of 0-22.00 μM, and large Stokes shift (243 nm). Additionally, PyS can serve as a paper, cotton swab, and polysulfone capsule kit for qualitative detection of Hg2⁺, enabling on-site quantitative detection of Hg2⁺ in beach soil and water samples using a smartphone app. It also can effectively detect Hg2⁺ in living cells in a concentration-dependent manner, thereby highlighting its potential for bioimaging in living organisms.

Bioorthogonally activated probes for precise fluorescence imaging

Over the past two decades, bioorthogonal chemistry has undergone a remarkable development, challenging traditional assumptions in biology and medicine. Recent advancements in the design of probes tailored for bioorthogonal applications have met the increasing demand for precise imaging, facilitating the exploration of complex biological systems. These state-of-the-art probes enable highly sensitive, low background, in situ imaging of biological species and events within live organisms, achieving resolutions comparable to the size of the biomolecule under investigation. This review provides a comprehensive examination of various categories of bioorthogonally activated in situ fluorescent labels. It highlights the intricate design and benefits of bioorthogonal chemistry for precise in situ imaging, while also discussing future prospects in this rapidly evolving field.

Development of Controllable Hetero-Pauson-Khand Polymerization to Functional Stimuli-Responsive Poly(γ-lactam)s

Polymers containing lactam structures play a crucial role in both natural biological systems and human life, and their synthesis, functions and applications are of utmost importance for biomimetics and the creation of new materials. In this study, we developed an efficient heterogeneous Pauson-Khand polymerization (h-PKP) method for the controlled synthesis of main-chain poly(γ-lactam)s containing α, β-unsaturated γ-lactam functionalities using readily available internal alkynes and imines. The molecular weights of the resulting poly(N-Ts/γ-lactam)s can be precisely controlled by adjusting the ratio of phenyl formate and nickel. These polymers exhibit high solid-state luminescence and demonstrate rapid and sensitive dual responsiveness to light and acid stimuli. They further demonstrate strong reactive oxygen species (ROS) generation capability. The unique dual-emission peaks observed in poly(N-H/γ-lactam)s obtained through post-treatment under acidic conditions demonstrate a mechanism of aggregation-induced intermolecular excited-state proton transfer specific to lactam structures. The efficient one-pot synthetic method for poly(γ-lactam) provides a novel strategy for constructing polymers with γ-lactam structures in the main chain and the simple and efficient post-modification method offer a versatile toolbox for functionalizing poly(γ-lactam)s to expand their potential applications.

Novel Perylene Diimide-Benzothaizole Hybrid: A Reaction-Based Probe for the Detection and Discrimination of H2S, Cys and DTT

The reaction-based probe perylene diimide-hydroxyphenyl benzothiazole (PR) can be used for the detection and discrimination of H2S, DTT and Cys in 20% HEPES buffer-DMSO and DMSO. The H2S induced radical anion formation of PR in 20% HEPES buffer and thiolysis of the ether bond of PR in DMSO. However, the addition of DTT showed only a decrease in the absorbance intensity and Cys showed insignificant behaviour towards PR in DMSO. The optical, AFM and DLS studies along with isolation of the reaction product in the model reaction support the interaction of the PR with bio thiols.

Excited-state antioxidant activity for apigenin based on external electric field-modulated ESIPT behavior: TD-DFT and molecular docking calculations

Apigenin (Api), a flavonoid possessing dual features of antioxidant activity and intramolecular hydrogen bond (IMHB), is subjected to an external electric field (EEF) to investigate its excited-state antioxidant activity after excited state intramolecular proton transfer (ESIPT) behavior employing the density functional theory (DFT) and time-dependent DFT (TD-DFT) methods, as well as molecular docking. The existence of IMHB is demonstrated by structural parameters and AIM topological analysis, where Api in the enol⁎ form under an EEF of +60 × 10-4 a.u. possesses strong IMHB. The potential energy curves confirm that the ESIPT process varies from barrierless to barriered as the positive EEF grows, thus determining the excited-state form. Api exhibits strong excited-state antioxidant activity in vitro whether or not under an EEF, especially under the EEF of -40 × 10-4 a.u., utilizing HOMO energy. According to average local ionization energy (ALIE), the electrophilic reaction site also changes after ESIPT process under the EEF, and the activity is significantly increased. Furthermore, activation of the antioxidant Keap1-Nrf2-ARE pathway in vivo, namely, the interaction of Keap1 protein with Api, calculated by molecular docking, suggests that an interaction between the Keap1 and excited-state Api exists accompanying lower and variable bind energy under the distinct EEFs. Taken together, combining the modulation of the ESIPT process with the excited-state antioxidant activity is an effective approach to enhance the antioxidant activity of compounds.

Coassembly of Dual-Modulated AIE-ESIPT Photosensitizers and UCNPs for Enhanced NIR-Excited Photodynamic Therapy

Aggregation-induced emission (AIE) photosensitizers are promising for photodynamic therapy, yet their short excitation wavelengths present a limitation. In this study, we develop a series of organic photosensitizers with dual modulation capabilities based on excited-state intramolecular proton transfer (ESIPT) and AIE. Notably, we synthesize near-infrared (NIR)-excited photosensitive nanoparticles through a coassembly strategy utilizing upconversion nanoparticles (UCNPs) and amphiphilic polymers. The spectroscopic analysis and theoretical calculations elucidate the significant impact of additional or π-spacer groups on the conformational change and the energy barrier of the ESIPT process. An efficient Förster resonance energy transfer between the photosensitizer and UCNPs is achieved through the coassembly strategy. Both in vitro and in vivo experiments demonstrate the antitumor efficacy of these nanoparticles under NIR excitation. This work not only introduces a novel approach for simultaneously modulating AIE properties and the ESIPT process but also provides a robust solution for overcoming the excitation wavelength limitations of many organic photosensitizers.

Small-Molecule Fluorescent Probes for Butyrylcholinesterase

Butyrylcholinesterase plays an indispensable role in organisms, and its abnormal expression poses a significant threat to human health and safety, covering various aspects including liver-related diseases, diabetes, obesity, cardiovascular and cerebrovascular diseases, and neurodegenerative diseases. In addition, toxic substances such as organophosphorus and carbamate pesticides markedly inhibit BChE activity. BChE activity serves as a critical parameter for the clinical diagnosis of acute organophosphorus pesticide poisoning and the evaluation of organophosphorus and carbamate pesticide residues. Therefore, the accurate and reliable detection of butyrylcholinesterase activity is particularly urgent and important for in-depth analysis of its biological function, diagnosis and therapy of related diseases, drug screening and sensitive detection of pesticide residues. Fluorescent probes have become a promising tool for sensing and imaging of butyrylcholinesterase, due to its advantages of high spatio-temporal resolution, high selectivity, non-invasive, high sensitivity, and tailored molecule structures. Here, this paper provides a comprehensive overview of the research progress in the sensing, imaging and therapy of butyrylcholinesterase utilizing fluorescent probes. This paper might be a useful guideline for researchers to design new high-performance fluorescence probes for BChE, and making further contributions to this intriguing field.

ESIPT fluorescence turn-on sensors for detection of short chain inorganic polyphosphate in water

We introduce two water-soluble excited state intramolecular proton transfer (ESIPT) based fluorescent turn-on probes responding to inorganic polyphosphates. These ESIPT probes enable specific detection of short-chain inorganic polyphosphates over a range of different condensed phosphates. The probes are weakly emissive in their off-state due to the blocking of ESIPT by Cu2+ coordination. Removal of the copper ion through decomplexation by the analyte accesses the on-state. The probes detect polyphosphates over other biologically occurring phosphates, pyrophosphate, and nucleotides such as ATP, ADP, GTP. An optimal fluorescence response is observed with the short-chain polyphosphate polyP8. Furthermore, the probe shows selectivity towards linear polyphosphates over cyclic metaphosphates. The rapid 'turn-off-turn-on' fluorescence responses upon consecutive addition of Cu2+ and polyP8 are reversible, further highlighting sensor performance in an aqueous environment. One of the sensors is then used to monitor polyP digestion by an exopolyphosphatase (PPX).

Advances in Natural-Product-Based Fluorescent Agents and Synthetic Analogues for Analytical and Biomedical Applications

Fluorescence is a remarkable property exhibited by many chemical compounds and biomolecules. Fluorescence has revolutionized analytical and biomedical sciences due to its wide-ranging applications in analytical and diagnostic tools of biological and environmental importance. Fluorescent molecules are frequently employed in drug delivery, optical sensing, cellular imaging, and biomarker discovery. Cancer is a global challenge and fluorescence agents can function as diagnostic as well as monitoring tools, both during early tumor progression and treatment monitoring. Many fluorescent compounds can be found in their natural form, but recent developments in synthetic chemistry and molecular biology have allowed us to synthesize and tune fluorescent molecules that would not otherwise exist in nature. Naturally derived fluorescent compounds are generally more biocompatible and environmentally friendly. They can also be modified in cost-effective and target-specific ways with the help of synthetic tools. Understanding their unique chemical structures and photophysical properties is key to harnessing their full potential in biomedical and analytical research. As drug discovery efforts require the rigorous characterization of pharmacokinetics and pharmacodynamics, fluorescence-based detection accelerates the understanding of drug interactions via in vitro and in vivo assays. Herein, we provide a review of natural products and synthetic analogs that exhibit fluorescence properties and can be used as probes, detailing their photophysical properties. We have also provided some insights into the relationships between chemical structures and fluorescent properties. Finally, we have discussed the applications of fluorescent compounds in biomedical science, mainly in the study of tumor and cancer cells and analytical research, highlighting their pivotal role in advancing drug delivery, biomarkers, cell imaging, biosensing technologies, and as targeting ligands in the diagnosis of tumors.

Visible-Light-Driven Solid-State Fluorescent Photoswitches for High-Level Information Encryption

Developing visible-light-driven fluorescent photoswitches in the solid state remains an enormous challenge in smart materials. Such photoswitches are obtained from salicylaldimines through excited-state intramolecular proton transfer (ESIPT) and subsequent cis-trans isomerization strategies. By incorporating a bulky naphthalimide fluorophore into a Schiff base, three photoswitches achieve dual-mode changes (both in color and fluorescence) in the solid state. In particular, the optimal one generates triple fluorescence changing from green, to yellow and finally to orange upon visible-light irradiation. This switching process is fully reversible and can be repeated at least 10 times without obvious attenuation, suggesting its good photo-fatigue resistance. Mechanism studies reveal that the naphthalimide group not only enables the tuning of multicolor with an additional emission, but also induces a folded structure, reducing molecular stacking and facilitating ESIPT and cis-trans isomerization. As such, photopatterning, ternary encoding and transient information recording and erasing are successfully developed. The present study provides a reliable strategy for visible-light-driven fluorescent photoswitches, showing implications for advanced information encryption materials.

AIE paper shred for the detection of evolved amine vapor from putrefaction processes of fish

Seafood plays a major role in the human diet. During transportation, without proper storage and supply chain, its quality deteriorates easily. The post-harvesting processes such as the storage of food play a crucial role in human health. So it is highly imperative to have a technique for identifying food spoilage earlier to ensure the food safety and security of the consumers. Herein we have developed a highly selective and sensitive fluorescent 'Turn-on' probe 2-amino-5-nitrobenzo [d] thiazol-2-yl) imino)methylphenol ANT based on aggregation induced emission (AIE). ANT molecule possesses both restricted intramolecular rotation (RIR) and excited state intramolecular proton transfer (ESIPT) properties leading to fluorescent enhancement rather than aggregation caused quenching (ACQ). The probe shows high selectivity and sensitivity towards the NH3 vapor. This probe with the AIE property is employed for the real-time detection of NH3 in both aqueous and gaseous phases. ANT molecule is deposited on the paper shred by a physical method is utilized to monitor NH3 vapor from red snapper fish as a real-time sample during its degradation processes. After two days there is a ratiometric color change in the paper shred from yellow to orange for the fish stored at room temperature indicating its rotten and unpalatability nature. Paper shred is reused by immersing it into the tetrahydrofuran (THF), in which it retains its initial color due to deprotonation of NH3, keto to enol tautomerism discloses the reusability of the fluorescent probe. Studies carried out using UV-visible and fluorescence spectroscopy infer that the ANT probe has high affinity towards NH3 vapor.

Biomass-derived multiatom-doped carbon dots for water sensing based on excited state intraparticle proton transfer in organic solvents

The presence of trace water impurities in organic solvents can significantly influence chemical reactions and product quality; thus, the accurate detection of water content in these solvents is a critical requirement for industrial applications. Accordingly, an eco-friendly, effective, and economical sensor for detecting trace quantities of miscible water in organic solvents is required for industrial applications. In this study, we synthesized biomass-derived multi-atom-doped carbon dots (MACDs) as fluorescent probes and employed them for the detection of trace amounts of water impurities in several water-miscible organic solvents. The MACDs exhibited stable dual-color fluorescence emission under ultraviolet light irradiation and red and blue emissions in organic solvents and water. The fluorescence quantum yield was approximately 11 %, which indicates an excited intraparticle proton transfer response due to an increase in the water content within a wide response range from 0 % to 100 % (v/v) in organic solvents. The intensity of the red emission signal at 670 nm gradually decreased with an increase in the water content in the organic solvent. The MACDs could detect water with an instant response time of 55 s, a high sensitivity, and low limits of detection of 0.08 %, 1.36 %, 0.03 %, 0.04 %, 0.12 %, and 0.05 % (v/v) in ethanol, acetonitrile, dimethylformamide, methanol, isopropanol, and tetrahydrofuran, respectively. Hence, biomass-derived MACDs can serve as efficient and eco-friendly water sensors in organic solvents.

The Golden Age of Thermally Activated Delayed Fluorescence Materials: Design and Exploitation

Since the seminal report by Adachi and co-workers in 2012, there has been a veritable explosion of interest in the design of thermally activated delayed fluorescence (TADF) compounds, particularly as emitters for organic light-emitting diodes (OLEDs). With rapid advancements and innovation in materials design, the efficiencies of TADF OLEDs for each of the primary color points as well as for white devices now rival those of state-of-the-art phosphorescent emitters. Beyond electroluminescent devices, TADF compounds have also found increasing utility and applications in numerous related fields, from photocatalysis, to sensing, to imaging and beyond. Following from our previous review in 2017 ( Adv. Mater. 2017, 1605444), we here comprehensively document subsequent advances made in TADF materials design and their uses from 2017-2022. Correlations highlighted between structure and properties as well as detailed comparisons and analyses should assist future TADF materials development. The necessarily broadened breadth and scope of this review attests to the bustling activity in this field. We note that the rapidly expanding and accelerating research activity in TADF material development is indicative of a field that has reached adolescence, with an exciting maturity still yet to come.

A Simple and Rapid "Turn-On" Fluorescent Probe Based on Binuclear Schiff Base for Zn2+ and Its Application in Cell Imaging and Test Strips

A series of colorful binuclear Schiff bases derived from the different diamine bridges including 1,2- ethylenediamine (bis-Et-SA, bis-Et-4-NEt2, bis-Et-5-NO2, bis-Et-Naph), 1,2-phenylenediamine (bis-Ph-SA, bis-Ph-4-NEt2, bis-Ph-5-NO2, bis-Ph-Naph), dicyano-1,2-ethenediamine (bis-CN-SA, bis-CN-4-NEt2, bis-CN-5-NO2, bis-CN-Naph) have been designed and prepared. The optical properties of these binuclear Schiff base ligands were fully determined by UV-Vis absorption spectroscopy, fluorescence emission spectroscopy, and time-dependent-density functional theory (TD-DFT) calculations. The inclusion of D-A systems and/or π-extended systems in these binuclear Schiff base ligands not only enables adjustable RGB light absorption and emission spectra (300~700 nm) but also yields high fluorescence quantum efficiencies of up to 0.84 in MeCN solution. Then, with the ESIPT (excited-state intramolecular proton transfer) property, fluorescence analysis showed that the probe bis-Et-SA and bis-Ph-SA could recognize Zn2+ via the "turn on" mode in the MeCN solution. During the detection process, bis-Et-SA and bis-Ph-SA demonstrate rapid response and high selectivity upon the addition of Zn2+. The coordination of Zn2+ with the oxygen atom and Schiff base nitrogen atom in a tetrahedral geometry is confirmed by Job's plot, FT-IR, and 1H NMR spectroscopy. In addition, the paper test and Hela cells were successfully carried out to detect Zn2+. Moreover, the sensitivity of bis-Et-SA and bis-Ph-SA is much better than that of those Schiff base ligands containing only one chelating unit [O^N^N^O].

Fluorescence sensing techniques for quality evaluation of traditional Chinese medicines: a review

Traditional Chinese medicines (TCMs) are highly valued and widely used worldwide. However, their complex compositions and various preparation processes have brought considerable challenges to the quality evaluation of Chinese medicines. The traditional methods for TCM quality evaluation suffer from the problems of cumbersome sample preparation, a long detection time, low sensitivity, etc. A more efficient and accurate evaluation method is urgently needed to ensure the stability and reliability of the quality of TCMs. As an emerging analytical technology, a fluorescent probe has the advantages of high sensitivity, high selectivity, easy operation, etc. It is capable of generating a specific fluorescent signal response to specific components in traditional Chinese medicines, realizing rapid and accurate detection of target components, which effectively solves the many difficulties of traditional methods. The purpose of this paper is to discuss the application of fluorescent probes in the quality evaluation of traditional Chinese medicines and the challenges they face. By introducing the principles, advantages and specific application cases of fluorescent probe technology in the quality evaluation of traditional Chinese medicines, we hope to provide new and efficient analytical ideas for the quality evaluation of traditional Chinese medicines.

A dual experimental-theoretical perspective on ESPT photoacids and their challenges ahead

Photoacids undergo an increase in acidity upon electronic excitation, enabling excited-state proton transfer (ESPT) reactions. A multitude of compounds that allow ESPT has been identified and integrated in numerous applications, as is outlined by reviewing the rich history of photoacid research reaching back more than 90 years. In particular, achievements together with ambitions and challenges are highlighted from a combined experimental and theoretical perspective. Besides explicating the spectral signatures, transient ion-pair species, and electronic states involved in an ESPT, special emphasis is put on the diversity of methods used for studying photoacids as well as on the effects of the environment on the ESPT, illustrated in detail for 8-hydroxypyrene-1,3,6-trisulfonate (HPTS) and the naphthols as examples of prototypical photoacids. The development of exceptionally acidic super-photoacids and magic photoacids is subsequently discussed, which opens the way to applications even in aprotic solvents and provides additional insight into the mechanisms underlying ESPT. In the overview of highlights from theory, a comprehensive picture of the scope of studies on HPTS is presented, along with the general conceptualization of the electronic structure of photoacids and approaches for the quantification of excited-state acidity. We conclude with a juxtaposition of established applications of photoacids together with potential open questions and prospective research directions.

Highly Potent Fluorenone Azine-based ESIPT Active Fluorophores for Cellular Viscosity Detection and Bioimaging Applications

Herein, synthesizes of fluorenone azine-based Schiff fluorescence probes: (E)-2-(((9H-fluoren-9-ylidene)hydrazineylidene)methyl)-5-(diethylamino)phenol (3a), (E)-9-(((9H-fluoren-9-ylidene)hydrazineylidene) methyl)-2,3,6,7-tetrahydro-1H,5H-pyrido[3,2,1-ij]quinolin-8-ol (3b), and (E)-1-(((9H-fluoren-9-ylidene)hydrazineylidene)methyl) naphthalen-2-ol (3c). The probes were structurally characterized using Fourier-transform infrared spectroscopy (FTIR), 1H and 13C nuclear magnetic resonance (NMR) spectroscopy and high-resolution mass spectrometry (HRMS) analysis. The probes exhibit hydrogen bonding between phenolic -OH and imine nitrogen, enabling excited state intramolecular proton transfer (ESIPT) and free rotation in the azine (> C = N-N = C <) functional, facilitating twisted intramolecular charge transfer (TICT), and a positive solvatochromism in solvent-dependent emission studies. Further, density functional theory (DFT) based calculations accounted for the observed photophysical TICT and ESIPT processes, revealing a non-covalent interaction between phenolic -OH and imine nitrogen. Furthermore, the fluorescence intensity (log I) showed good linearity (R2 = 0.999) with the viscosity (log η) with Förster-Hoffmann coefficient (X) values of 2.238, 1.405 and 3.121 for 3a, 3b and 3c, respectively. The study established the probes toxicity and fluorescence imaging in the Caenorhabditis elegans model. Probe 3a, the first azine-based probe for micro viscosity detection, demonstrated exceptional efficacy in detecting intercellular viscosity and facilitating bioimaging applications.

Excited-state intramolecular proton transfer (ESIPT) active interwoven polycatenated coordination polymer for selective detection of Al3+ and Ag+ ions along with water detection in less polar solvents

The external stimuli-responsive excited-state intramolecular proton transfer (ESIPT) on/off mechanism is a unique and expedient sensing method that offers easy monitoring through the transition between dual and single-peak emissions. To avail this advantage of ESIPT-based sensing for selective metal ion detection and trace water detection, we have synthesized a 2,5-dihydroxyterephthalate (dht)-based interwoven polycatenated coordination polymer (1). The synthesized compound has been thoroughly characterized using single-crystal and powder X-ray diffraction techniques, along with other physicochemical methods. The synthesized compound exhibits a visual luminescence color change from faint yellow to bright green under UV irradiation in the presence of Al3+ ions. This change is attributed to a blue shift in fluorescence maxima of the keto form of the dht ligand in contact with Al3+ ions. Additionally, the material detects Ag+ ions through an ESIPT-off mechanism. These significant changes in ESIPT - blue shifting for Al3+ and ESIPT-off for Ag+ - start in just 1 mM aqueous solutions of these ions. Significantly, the ESIPT-off for Ag+ is evident even in the presence of other interfering ions. Beyond metal ion detection, this material also offers both qualitative and quantitative sensing of trace amounts of water in various polar organic solvents, such as ethanol (EtOH), tetrahydrofuran (THF), isopropanol (IPA), acetone, and acetonitrile (ACN), through the ESIPT-on/off phenomenon. The activated framework of compound 1 (1') can detect 2%, 4%, 4%, 3%, and 3% water in acetone, ACN, EtOH, IPA, and THF, respectively; through the conversion from a single to dual hump emission alteration. The respective ESIPT peak shift and ESIPT-on/off in the presence of metal ions and water is explained by the interaction between the host coordination polymer and guest analytes.

Multicomponent Diversity-Oriented Access to Boronic-Acid-Derived Pyrrolide Salicyl-Hydrazone Fluorophores with Strong Solid-State Emission

Fluorescent molecular platforms are highly sought after for their applications in biology and optoelectronics but face challenges with solid-state emission quenching. To address this, bulky substituents or aggregation-induced emission luminogens to restrict intramolecular motion are used to enhance the brightness. Here, we have successfully engineered a novel class of boron complexed pyrrolide salicyl-hydrazone fluorophores named BPSHY. These dyes were synthesized through a diversity-oriented condensation of pyrrole and salicylaldehyde derivatives combined with various aromatic boronic acids. The resulting 3D structures, owing to bulky boron axially substituted aryl groups, impart excellent solubility in a variety of solvents. Significantly, the BPSHY dyes exhibit strong absorption in the visible region and remarkably large Stokes shifts. Crucially, they demonstrate intense emission in aqueous solutions due to aggregation-induced emission effects. In solid-states, these dyes achieve high quantum yields, reaching up to 58%. Further expanding their utility, we developed two new BPSHY probes: one incorporating morpholine and another containing triphenylphosphine salt. Both of them are found to specifically label subcellular organelles such as lysosomes and mitochondria within live cells. Notably, these probes demonstrate exceptional staining efficacy and two-photon fluorescence feature. This highlights the considerable promise of BPSHY fluorophores for monitoring and visualizing the dynamic transformations of organelles.

Catalyst-free and wavelength-tuned glycosylation based on excited-state intramolecular proton transfer

The chemoselectivity of organic reactions is a fundamental topic in organic chemistry. In the long history of chemical synthesis, achieving chemoselectivity is mainly limited to thermodynamic conditions by an exogenous activation strategy. Here, we design an endogenous activation method, which can be used to control the chemoselectivity of phenol and naphthol through the photo-induced excited-state intramolecular proton transfer (ESIPT). A wavelength-tuned glycosylation is developed to showcase the penitential of this new strategy. Traditionally, an exogenous activator (electrophilic promoters) is essential to induce the cleave of a polar single bond, and this strategy has been extensively studied and used in the glycosylation chemistry, for the formation of oxocarbenium cation intermediate. In our systems, the oxocarbenium cation intermediates can be selectively formed from glycosyl donors bearing tunable chromophoric groups under mild conditions of acid-base free and redox neutrality, which enables continuous synthesis of oligosaccharides.

Novel ratiometric fluorescent probe with large Stokes shift for selective sensing and imaging of Zn2+ in live cell

A novel ratiometric fluorescent probe, namely 5-[(3-dicyanoylidene -5.5-dimethyl) cyclohexenyl-1-ethenyl] salicylaldehyde-3'-hydroxybenzohydrazone (DCSH) is presented for the selective sensing of Zn2+ ion in acetonitrile/water (2/3, pH 7.4) solution. Introducing Zn2+ ions notably caused the peak emission of DCSH to shift from 560 nm to 646 nm, accompanied with a significant enhancement of its intensity. A vivid change in fluorescence color from yellow to red facilitated the immediate identification of Zn2+ ions by visual observation. DCSH exhibits substantial Stokes shifts (110 and 196 nm), rapid detection capability (within 10 s) and high sensitivity to Zn2+ ions, achieving a limit of detection of 31.2 nM. The response mechanism is supposed to involve the block of C = N bond isomerization and excited state intramolecular proton transfer (ESIPT) along with the enhancement of fluorescence through chelation (CHEF) effect. DCSH was effectively utilized for ratiometric fluorescence imaging to monitor exogenous Zn2+ concentrations in HeLa cells. Significantly, DCSH is capable of monitoring elevated levels of Zn2+ ion during apoptosis induced by L-Buthionine sulfoximine (BSO).

A Novel Benzothiazole-Based Fluorescent AIE Probe for the Detection of Hydrogen Peroxide in Living Cells

A benzothiazole-based derivative aggregation-induced emission (AIE) fluorescent 'turn-on' probe named 2-(2-((4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)benzyl)oxy)phenyl)benzo[d]thiazole (probe BT-BO) was developed and synthesized successfully for detecting hydrogen peroxide (H2O2) in living cells. The synthesis method of probe BT-BO is facile. Probe BT-BO demonstrates a well-resolved emission peak at 604 nm and the ability to prevent the interference of reactive oxygen species (ROS), various metal ions and anion ions, and good sensitivity. Additionally, the probe boasts impressive pH range versatility, a fast response time to H2O2 and low cytotoxicity. Finally, probe BT-BO was applied successfully to image A549 and Hep G2 cells to monitor both exogenous and endogenous H2O2.

Tunable Emission and Structural Insights of 6-Arylvinyl-2,4-bis(2'-hydroxyphenyl)pyrimidines and Their O∧N∧O-Chelated Boron Complexes

In this study, we present the synthesis and photophysical characteristics of a novel series of 6-arylvinyl-2,4-bis(2'-hydroxyphenyl)pyrimidines. These compounds exhibit nonemissive properties attributed to the potential occurrence of a excited-state intramolecular proton transfer process from the OH groups to the nitrogen atoms of the pyrimidine ring. The introduction of an acid for protonation of the pyrimidine ring results in a significant enhancement of the fluorescence response, easily perceptible to the naked eye. Notably, these molecules serve as intriguing rigid O∧N∧O ligands for boron chelation. The incorporation of boron atoms promotes structural planarity, increases rigidity, and successfully restores fluorescence in both solution and the solid state. Moreover, the photoluminescence was found to be strongly influenced by the nature of the end groups on the arylvinylene fragment, allowing for the modulation of the emission color and covering the optical spectrum from blue to red. Strong emission solvatochromism was observed in various solvents, a finding that supports the formation of intramolecular charge-separated emitting states, particularly when terminal electron-donating groups are present in the structure. X-ray diffraction analysis enables the determination of inter- and intramolecular interactions, as well as molecular packing structures, aiding in the rationalization of distinct luminescent behaviors in the solid state. All experimental findings are elucidated through extensive density functional theory (DFT) and time-dependent DFT calculations.

Recognition of specific monosaccharides by fluorescence change through the suppression effect on excited-state intermolecular proton transfer reactions

Pyrene-urea derivatives and acetate anions were used to investigate the excited-state intermolecular proton transfer (ESPT) reaction, where a molecule undergoes intermolecular proton transfer to form a tautomer species in the excited state. Since ESPT occurs when intermolecular hydrogen bonds exist between urea compounds and acetate species, we hypothesize that this reaction might be influenced by compounds with hydroxy groups. In this study, cyclodextrins, saccharides, and ethanol were examined to assess the effects of hydroxy groups on the ESPT reaction. After introducing various hydroxy compounds into the urea-acetate system in dimethylformamide, we observed differences in the fluorescence spectra and fluorescence decay curves. These differences indicate varying interactions between the hydroxy compounds and complexes, leading to distinct fluorescence lifetime behaviors, which makes fluorescence lifetime imaging technology particularly suitable.

Extending Non-Perturbative Simulation Techniques for Open-Quantum Systems to Excited-State Proton Transfer and Ultrafast Non-Adiabatic Dynamics

Excited state proton transfer is an ubiquitous phenomenon in biology and chemistry, spanning from the ultrafast reactions of photobases and acids to light-driven, enzymatic catalysis and photosynthesis. However, the simulation of such dynamics involves multiple challenges, since high-dimensional, out-of-equilibrium vibronic states play a crucial role, while a fully quantum description of the proton's dissipative, real-space dynamics is also required. In this work, we extend the powerful matrix product state approach to open quantum systems (TEDOPA) to study these demanding dynamics, and also more general nonadiabatic processes that can appear in complex photochemistry subject to strong laser driving. As an illustration, we initially consider an open model of a four-level electronic system interacting with hundreds of intramolecular vibrations that drive ultrafast excited state proton transfer, as well as an explicit photonic environment that allows us to directly monitor the resulting dual fluorescence in this system. We then demonstrate how to include a continuous "reaction coordinate" of the proton transfer that allows numerically exact simulations that can be understood, visualized and interpreted in the familiar language of diabatic and adiabatic dynamics on potential surfaces, while also retaining an exact quantum treatment of dissipation and driving effects that could be used to study diverse problems in ultrafast photochemistry.

An elegant approach for the synthesis of multisubstituted imidazole via FeCl3/SiO2 catalyzed activation of acetals: a photophysical study of an imidazole-carbazole hybrid

A simple and solvent-free catalytic system was developed for the direct conversion of multisubstituted imidazoles through the reaction of acetals and benzils with ammonium acetate/amines as the source of nitrogen. The reaction occurred under mild and benign conditions using FeCl3/SiO2 as a heterogeneous catalyst without the requirement of any toxic organic solvents. The easy preparation and recyclability of the catalyst allows the reaction to be simple and highly efficient, resulting in very good yields of imidazoles. Novel imidazole-carbazole hybrid compounds were also synthesised by adopting the present methodology. Single crystal X-ray diffraction study indicated the presence of a CH⋯π supramolecular interaction that renders effective molecular packing in the solid state. The steady-state and spectro-dynamic behaviours of these hybrid molecules were investigated, and it was revealed that a solvent-dependent excimer-coupled ICT phenomenon guided excited state photophysics. Very unusual excimer lifetime was noticed in the solid state of this bis-heterocyclic compound owing to the stacking of molecules via CH⋯π interaction, as evident from the X-ray studies.

Recent advances in fluorescent probes for fatty liver imaging by detecting lipid droplets

Fatty liver, a major health problem worldwide, is closely associated with aberrant accumulation and alteration of energy storage organelles, lipid droplets (LDs), in the disease process. Fluorescent probes with excellent optical performance, high sensitivity/selectivity and real-time monitoring have emerged as an attractive tool for the detection of LDs used in the diagnosis of fatty liver. In this review, we summarize various probes based on different response mechanisms to image LDs in the fatty liver process using different excitation imaging modes and emission wavelengths, including the visible to the near-infrared, two/three-photon, and the second near-infrared region. The perspectives and barriers associated with the reported lipid droplet (LD) probes for future development are also discussed.

Photoexcitation Dynamics of 4-Aminopthalimide in Solution Investigated Using Femtosecond Time-Resolved Infrared Spectroscopy

Excited-state intramolecular proton transfer (ESIPT) reactions are crucial in photoresponsive materials and fluorescent markers. The fluorescent compound 4-aminophthalimide (4-AP) has been reported to exhibit solvent-assisted ESIPT in protic solvents, such as methanol, wherein the solvent interacts with 4-AP to form a six-membered hydrogen-bonded ring that is strengthened upon excitation. Although the controversial observation of ESIPT in 4-AP has been extensively studied, the molecular mechanism has yet to be fully explored. In this study, femtosecond infrared spectroscopy was used to investigate the dynamics of 4-AP in methanol and acetonitrile after excitation at 350 and 300 nm, which promoted 4-AP to the S1 and S2 states, respectively. The excited 4-AP in the S1 state relaxed to the ground state, while 4-AP in the S2 state relaxed via the S1 state without the occurrence of ESIPT. The enol form of 4-AP (Enol 4-AP) in the S1 state was calculated to be ~10 kcal/mol higher in energy than the keto form in the S1 state, indicating that keto-to-enol tautomerization was endergonic, ultimately resulting in no observable ESIPT for 4-AP in the S1 state. Upon the excitation of 4-AP to the S2 state, the transition to Enol-4-AP in the S1 state was found to be exergonic; however, ESIPT must compete with an internal conversion from the S2 to the S1 state. The internal S2 → S1 conversion was significantly faster than the solvent-assisted ESIPT, resulting in a negligible ESIPT for the 4-AP excited to the S2 state. The detailed excitation dynamics of 4-AP clearly reveal the molecular mechanism underlying its negligible ESIPT, despite the fact that it forms a favorable structure for solvent-assisted ESIPT.

Stimuli-Induced Fluorescence Switching in Azine-Containing Fluorophores Displaying Resonance-Stabilized ESIPT Emission

This article reports the synthesis, along with structural and photophysical characterization of 2-(2'-hydroxyphenyl)benzazole derivatives functionalized with various azaheterocycles (pyridine, pyrimidine, terpyridine). These compounds show dual-state emission properties, that is intense fluorescence both in solution and in the solid-state with a range of fluorescent color going from blue to orange. Moreover, the nature of their excited state can be tuned by the presence of external stimuli such as protons or metal cations. In the absence of stimuli, these dyes show emission stemming from anionic species obtained after deprotonation (D* transition), whereas upon protonation or metal chelation, ESIPT process occurs leading to a stabilized and highly emissive K* transition. With the help of extensive ab initio calculations, we confirm that external stimuli can switch the nature of the transitions, making this series of dyes attractive candidates for the development of stimuli-responsive fluorescent ratiometric probes.

Fluorescent response mechanism based on ESIPT and TICT of novel probe H2QJI: A TD-DFT investigation

Recently, synthesized N-linked-disalicylaldehyde H2QJI probes have been used to detect heavy metal ions in the experiment conveniently. Nevertheless, there needs to be a more in-depth examination of the excited state intramolecular proton transfer (ESIPT) mechanism and photophysical properties of the probe. This work remedied it based on quantum chemistry calculations. We contained due hydrogen bond (O1-H2 ⋯ N3 and O4-H5 ⋯ O6) and then analyzed bond parameters, IR vibration spectra, and non-covalent interaction. The bond strength is enhanced under photoexcitation, and the former is significantly stronger. The calculated electron spectra are in agreement with the experimental values. The results of the S0 and S1 potential energy curves and IRC calculations also confirm the unique ESIPT behavior, which isan excited stated stepwise double proton transfer. The fluorescence, internal conversion, and intersystem crossing rate of KD molecules (twisted-, double proton transfer) were calculated respectively to reveal the radiative and non-radiative pathways. It proved that the corresponding spectra are not obtained since the electrons are mainly deactivated by the ISC (S1->T1). Furthermore, the interfragment charge transfer (IFCT) approach indicates that the molecule possesses twisted intramolecular charge transfer (TICT) characteristics, which lead to the quenching of fluorescence introduction.

Excitation wavelength-dependent fluorescence anisotropy of 3-hydroxyflavone: revisiting the solvation processes and high-energy state excitation in ESIPT-active compounds

To gain a more comprehensive understanding of the phenomenon of high-fluorescence anisotropy of the normal form emission of ESIPT-active compounds in protic solvents, excitation wavelength dependence of emission anisotropy was investigated for 3-hydroxyflavone (3HF) using steady-state spectroscopic technique and quantum chemical calculations. It was shown for the first time that the anisotropy of 3HF normal form emission is characterized by significant dependence on excitation energy. Experimental results indicate that the fluorescence anisotropy of 3HF in methanol (at 20 °C) changes abruptly from about 0.18 to about 0.10 with a decrease in excitation wavelength. This spectroscopic phenomenon can be explained by two factors: (1) breaking of intermolecular solute-solvent hydrogen bonds upon photoexcitation and (2) excitation of ESIPT-active fluorophores to the second singlet state (S2). The results of quantum chemical calculations clearly indicate that specific hydrogen bonding solvation interactions can lead to the formation of 3HF-methanol complexes with larger molecular volumes than the volume of free 3HF molecule. High excitation energy can reform and break solute-solvent bonds, which leads to a decrease in molecular system volume. This results in a decrease in rotational correlation time and fluorescence anisotropy. As is known, the fluorescence lifetime of small-sized molecules is closely correlated with the conformational changes in the excited state, and in the case of ESIPT-active compounds, the lifetime of normal form emission is almost fully determined by the ultrafast ESIPT process. Therefore, although in general, fluorescence lifetime is considered independent of excitation energy, but because the timescale of ESIPT processes is of the same order as the timescale of internal conversion, in the case of ESIPT-active compounds, fluorescence lifetime changes caused by high-energy state excitation cannot be neglected. The emission anisotropy of the normal form of an ESIPT-active compound will decrease with an increase in fluorescence lifetime caused by an increase in excitation energy sufficient to excite molecules to higher electronic states. In this work, both hypotheses are discussed and verified using experimental data and quantum chemical calculations for 3HF in methanol.

Flexible organic crystals with multi-stimuli-responsive CPL for broadband multicolor optical waveguides

Flexible organic crystals, capable of transmitting light and responding to various external stimuli, are emerging as a new frontier in optoelectronic materials. They hold immense potential for applications in molecular machines, sensors, displays, and intelligent devices. Here, we report on flexible organic crystals based on single-component enantiomeric organic compounds, demonstrating multi-stimuli-responsive circularly polarized light (CPL). These crystals exhibit remarkable elasticity, responsiveness to light and acid vapors, and tunable circularly polarized optical signals. Upon exposure to acid vapors, the fluorescence of the crystals shifts from initial yellow emission to green emission, attributable to the protonation-induced inhibition of excited-state intramolecular proton transfer. Under UV irradiation, the fluorescence emission undergoes a red-shift, resulting from the molecular transformation from an enol configuration to a ketone configuration. Notably, both processes are reversible and can be restored under daylight. The integration of reversible fluorescence changes under light and acid vapors stimuli, CPL signals, and flexible optical waveguides within a single crystal paves the way for the application of organic crystals as all-organic chiral functional materials.

Theoretical Investigations on the Sensing Mechanism of Dicyanoisophorone Fluorescent Probe for the Detection of Hydrogen Sulfide

As one of the biomolecules, hydrogen sulfide (H2S) has received a lot of attention. Recent studies have shown that endogenous hydrogen sulfide plays different roles in different organs in biological systems. Fluorescent probe technology has been widely adopted due to its many advantages such as low cost, simple operation, and high sensitivity. Among many probes, dicyanoisophorone fluorophore is often used in probe design for real-time detection of endogenous H2S due to the large Stokes shift and long fluorescence emission wavelength. In this paper, the fluorescence sensing mechanism of dicyanoisophorone-like probe L and its product 3 with near-infrared fluorescence emission has been theoretically investigated by using theory methods. The analysis of infrared (IR) vibration spectra and reduced density gradient (RDG) showed that the hydrogen bond of the enolic structure of product 3 was significantly enhanced in the S1 state. The spectroscopic information revealed that the emission of NIR fluorescence originated from the keto structure of the product. Finally, potential energy curves and frontier molecular orbitals diagrams showed that the fluorescence quenching phenomenon of the probe L was attributed to the photoinduced electron transfer (PET) process, whereas the product 3 generated after the detection of H2S undergoes the excited state intramolecular proton transfer (ESIPT) process.

Advances in small-molecule fluorescent probes for the study of apoptosis

Apoptosis, as type I cell death, is an active death process strictly controlled by multiple genes, and plays a significant role in regulating various activities. Mounting research indicates that the unique modality of cell apoptosis is directly or indirectly related to different diseases including cancer, autoimmune diseases, viral diseases, neurodegenerative diseases, etc. However, the underlying mechanisms of cell apoptosis are complicated and not fully clarified yet, possibly due to the lack of effective chemical tools for the nondestructive and real-time visualization of apoptosis in complex biological systems. In the past 15 years, various small-molecule fluorescent probes (SMFPs) for imaging apoptosis in vitro and in vivo have attracted broad interest in related disease diagnostics and therapeutics. In this review, we aim to highlight the recent developments of SMFPs based on enzyme activity, plasma membranes, reactive oxygen species, reactive sulfur species, microenvironments and others during cell apoptosis. In particular, we generalize the mechanisms commonly used to design SMFPs for studying apoptosis. In addition, we discuss the limitations of reported probes, and emphasize the potential challenges and prospects in the future. We believe that this review will provide a comprehensive summary and challenging direction for the development of SMFPs in apoptosis related fields.

Color-tunable and white circularly polarized luminescence through confining guests into chiral MOFs

Herein, chiral metal-organic frameworks (MOFs), DCF-20 and LCF-20, were utilized as matrices for both chirality transfer and energy transfer. HBT1@MOFs and HBT2@MOFs emit excitation-dependent circularly polarized luminescence (CPL) due to excited-state intramolecular proton transfer (ESIPT). HBT1/C152/NIR@MOFs exhibit full-color and white CPL. The luminescence dissymmetry factors (glum) were significantly increased, benefiting from the efficient chirality space transfer and high luminescence efficiency.

Aggregation-Induced Emission Enhancement and Solid-State Photoswitching of Crystalline Carbazole N-Salicylidene Anilines

The development of fluorescent stimuli-responsive organic materials has attracted substantial interest due to their increasing optoelectronic applications. This study systematically introduces fluorine atoms on one end of carbazole-based N-salicylidene anilines 5a-5f to elucidate the impact in their solution and solid-state photophysics. The addition of fluorine atoms at one end of the molecule induced significant changes, for example, a reduction in the quantum yield (QY) fluorescence emission in solution, going from QY near unity in compound 5a (QY ∼ 100%) to a negligible emission in 5f (QY < 1%). Similarly, compound 5a showed a very strong aggregation-induced enhancement emission behavior, whereas compounds with a higher fluorine content were almost quenched. Furthermore, the crystalline solid-state photoisomerization in N-salicylidene anilines is not trivial, and only compounds with three (5e) and five fluorine atoms (5f) exhibited reversible solid-state photoisomerization under 405 nm light source irradiation. We propose that the presence of the arene-perfluoroarene interaction in the crystalline array facilitates the latter behavior. Our findings present a comprehensive study of crystal engineering for the obtention of photoswitchable crystalline materials and adjustable photophysics response, paving the way for its implementation in other systems.

2D Conjugated Polymer Thin Films for Organic Electronics: Opportunities and Challenges

2D conjugated polymers (2DCPs) possess extended in-plane π-conjugated lattice and out-of-plane π-π stacking, which results in enhanced electronic performance and potentially unique band structures. These properties, along with predesignability, well-defined channels, easy postmodification, and order structure attract extensive attention from material science to organic electronics. In this review, the recent advance in the interfacial synthesis and conductivity tuning strategies of 2DCP thin films, as well as their application in organic electronics is summarized. Furthermore, it is shown that, by combining topology structure design and targeted conductivity adjustment, researchers have fabricated 2DCP thin films with predesigned active groups, highly ordered structures, and enhanced conductivity. These films exhibit great potential for various thin-film organic electronics, such as organic transistors, memristors, electrochromism, chemiresistors, and photodetectors. Finally, the future research directions and perspectives of 2DCPs are discussed in terms of the interfacial synthetic design and structure engineering for the fabrication of fully conjugated 2DCP thin films, as well as the functional manipulation of conductivity to advance their applications in future organic electronics.

AI-Powered Mining of Highly Customized and Superior ESIPT-Based Fluorescent Probes

Excited-state intramolecular proton transfer (ESIPT) has attracted great attention in fluorescent sensors and luminescent materials due to its unique photobiological and photochemical features. However, the current structures are far from meeting the specific demands for ESIPT molecules in different scenarios; the try-and-error development method is labor-intensive and costly. Therefore, it is imperative to devise novel approaches for the exploration of promising ESIPT fluorophores. This research proposes an artificial intelligence approach aiming at exploring ESIPT molecules efficiently. The first high-quality ESIPT dataset and a multi-level prediction system are constructed that realized accurate identification of ESIPT molecules from a large number of compounds under a stepwise distinguishing from conventional molecules to fluorescent molecules and then to ESIPT molecules. Furthermore, key structural features that contributed to ESIPT are revealed by using the SHapley Additive exPlanations (SHAP) method. Then three strategies are proposed to ensure the ESIPT process while keeping good safety, pharmacokinetic properties, and novel structures. With these strategies, >700 previously unreported ESIPT molecules are screened from a large pool of 570 000 compounds. The ESIPT process and biosafety of optimal molecules are successfully validated by quantitative calculation and experiment. This novel approach is expected to bring a new paradigm for exploring ideal ESIPT molecules.

Ex Tenebris Lux: Illuminating Reactive Oxygen and Nitrogen Species with Small Molecule Probes

Reactive oxygen and nitrogen species are small reactive molecules derived from elements in the air─oxygen and nitrogen. They are produced in biological systems to mediate fundamental aspects of cellular signaling but must be very tightly balanced to prevent indiscriminate damage to biological molecules. Small molecule probes can transmute the specific nature of each reactive oxygen and nitrogen species into an observable luminescent signal (or even an acoustic wave) to offer sensitive and selective imaging in living cells and whole animals. This review focuses specifically on small molecule probes for superoxide, hydrogen peroxide, hypochlorite, nitric oxide, and peroxynitrite that provide a luminescent or photoacoustic signal. Important background information on general photophysical phenomena, common probe designs, mechanisms, and imaging modalities will be provided, and then, probes for each analyte will be thoroughly evaluated. A discussion of the successes of the field will be presented, followed by recommendations for improvement and a future outlook of emerging trends. Our objectives are to provide an informative, useful, and thorough field guide to small molecule probes for reactive oxygen and nitrogen species as well as important context to compare the ecosystem of chemistries and molecular scaffolds that has manifested within the field.

Aggregation-induced emissive nanoarchitectures for luminescent solar concentrators

Aggregation-induced emission (AIE), the phenomenon by which selected luminophores undergo the enhancement of emission intensity upon aggregation, has demonstrated potential in materials and biomaterials science, and in particular in those branches for which spectral management in the solid state is of fundamental importance. Its development in the area of luminescent spectral conversion devices like luminescent solar concentrators (LSCs) is instead still in its infancy. This account aims at summarizing relevant contributions made in this field so far, with a special emphasis on the design of molecular and macromolecular architectures capable of extending their spectral breadth to the deep-red (DR) and the near-infrared (NIR) wavelengths. Because of the many prospective advantages characterizing these spectral regions in terms of photon flux density and human-eye perception, it is anticipated that further development in the design, synthesis and engineering of advanced molecular and macromolecular DR/NIR-active AIE luminophores will enable faster and easier integration of LSCs into the built environment as highly transparent, active elements for unobtrusive light-to-electricity conversion.

Theoretical Study on the Effect of Cyano- and Dimethylamine-Group on ESIPT Behavior and Luminescent Properties of Novel Flavone-Based Fluorophore

Recently, a new fluorescent senor based on 3-hydroxy-2-(naphthalen-2-yl)-4 H-chromen-4-one (HFN) for selective detection of H2Sn was obtained in the experiment (Spectrochim. Acta Part A 271(2022)120962). Based on HFN, three new compounds (HFN1, HFN2 and HFN3) are designed to explore the influences of dimethylamine (-N(CH3)2) and cyano (-CN) groups on the excited-state intramolecular proton transfer (ESIPT) process and luminescent features of HFN. After analyzing the mainly geometrical parameters, electron densities and infrared spectra, we discovered that the intramolecular hydrogen bonds (IHBs) in the target molecules become stronger upon photo-excitation. Introducing -CN or/and -N(CH3)2 groups into HFN indeed influences its ESIPT behavior and luminescent properties. The -N(CH3)2 group enhances IHB, reduces ESIPT barrier and caused absorption/ fluorescence (at T form) peak blue-shift, while the -CN group shows a counterproductive effect. The coincidence of -N(CH3)2 and -CN made the absorption/fluorescent wavelength of HFN red-shift more than single -N(CH3)2 or -CN group does.